feat(P6/T04): WidgetAdapterSpecsController, registry, widget adapter integration

CRUD for WidgetAdapterSpec (index, show, new/create, edit/update — status+notes only
after creation). Widget new/edit forms expose optional adapter_spec_id select.
Widget show page renders adapter badge with link to spec. Widgets controller
fetches adapter spec for show action.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Web/View/Widgets/Edit.hs

@@ -7,8 +7,9 @@ import IHP.ViewPrelude
 import Web.View.Widgets.New (renderForm)
 
 data EditView = EditView
-    { widget :: !Widget
-    , hubs   :: ![Hub]
+    { widget       :: !Widget
+    , hubs         :: ![Hub]
+    , adapterSpecs :: ![WidgetAdapterSpec]
     }
 
 instance View EditView where
@@ -22,6 +23,6 @@ instance View EditView where
                 <span>Edit</span>
             </div>
             <h1 class="text-2xl font-semibold mb-6">Edit Widget</h1>
-            {renderForm widget hubs}
+            {renderForm widget hubs adapterSpecs}
         </div>
     |]